HIGH-PRESSURE STUDY OF THE VISCOSITY EFFECT ON THE GROUND-STATE ISOMERIZATION OF 3,3'-DIETHYLOXADICARBOCYANINE IODIDE (DODCI)

The viscosity dependence on the ground-state isomerization of DODCI was studied as a model of one-dimensional barrier crossing by using a technique of high-pressure laser photolysis. The Kramers equation does not fit the data over the whole viscosity range examined. We show how our results are reproduced by the Grote and Hynes theory where frequency-dependent friction is considered for describing the influence of solvent friction. Solvent viscosity contributions to the apparent activation energy and apparent activation volume are discussed. The intrinsic activation energy of isomerization is 13.0 kcal/mol. The apparent activation volume can be explained exclusively by the volume change due to viscous flow. The intrinsic activation volume is found to be less than 1.0 cm3/mol.